Six years experience with Offset pole-dipole and other 3D IP arrays. What have we learnt?

Abstract

It is now more than six years since the initial tests of pole-dipole IP that led to the development of the offset pole-dipole array were carried out at Copper Hill in NSW. In this period, the authors have been involved in more than 50 similar surveys world wide including a complete resurvey of the Copper Hill prospect using a more advanced `production' style configuration. Numerous practical lessons have been learnt through the progress of these surveys. Different methods of electrode emplacement, array geometry and electrode types have been evaluated both in the field and through modelling. A study of safety considerations led to the recognition of the importance for extremely good ground contact for remote electrodes in pole-dipole surveys, not only to boost the transmitter current but also to lower the electrical potential of the remote wire to avoid fire and shock hazards. The pitfalls of 3D configurations where the receiver dipole lies close to an equipotential were not widely appreciated in early surveys but it has been found that these can result in spurious anomalies that may be very difficult to evaluate unless the problems are recognized early in the processing.